Introduction to Computer Networks

Course Objectives

• Students will learn the basic concepts of computer networks, including network architectures, protocols, and standards like TCP/IP, OSI model, LAN/WAN, and topologies.
• Students will understand the functions of core networking devices like routers, switches, bridges, and gateways and how they enable connectivity and communication.
• Students will analyze the trade-offs between connection-oriented and connectionless services, circuit switching vs packet switching, and other network technology comparisons.
• Students will design and configure local area networks with addressing schemes and routing/switching equipment tailored to meet networking requirements.
• Students will evaluate network protocol stacks to pinpoint common networking issues across physical, data link, and upper layer components.
• Students will troubleshoot connectivity, performance, and reliability issues using tools like ping, traceroute, and SNMP.
• Students will learn network troubleshooting methodologies
• Students will demonstrate understanding of network and infrastructure security issues and mitigation approaches.

Course Content

• Week 1: Introduction to networking
• Week 2: Local Area Network Protocols and Standards
• Week 3: Physical Media
• Week 4: IP Networks
• Week 5: Network Design and Simulation, IPv4
• Week 6: Mid Semester Exam
• Week 7 & 8: IPv6
• Week 9: Industrial Seminar
• Week 10 & 11: Network Security
• Week 12: Final Examination

Course Assessment

• Participation and Class Engagement accounts for 5% of the grade.
• Quizzes and Assignments make up 15%.
• Group Project is 10% of the grade.
• Mid-Semester Exams contribute 20%.
• Final Exam is weighed at 50%.
• Continuous Assessment will include Mid-Semester Exams (20%) and Quizzes and Assignments (10%), for a total of 30%.
• All other forms of Assessment will culminate into the End of Semester Score of 70%

Lecture 1: Introduction

• Topics include communication models, definitions of computer networks, LANs, WANs, ISO – OSI reference model, as well as network components and topologies.

Simplified Communication Model

• The primary goal of any communication system involves exchanging data between two points
• Source: Generates the data to be transmitted, e.g., phones and PCs.
• Transmitter: Transforms and encodes data into a suitable form for the transmission system.
• Transmission System: A single transmission line or a complex network connecting source and destination.
• Receiver: Accepts the signal from the transmission system and adapts it into a form suitable for the destination device.
• Destination: Receives the incoming data from the receiver.

Communication Networks

• Data communication occurs between two devices directly connected by a point-to-point transmission medium.
• A communication network is needed when devices can't be directly connected.
• Optical fibres have reduced transmission costs for telephone networks and increased capacities.
• Satellite communications have enhanced long-distance routes' information-carrying capacity.
• Advances in VLSI technology have led to powerful computers for telephone exchange control
• Mobile communication faces bandwidth constraints
• Computers increased data communications leading to interconnecting computers, terminals, printers at a local level
• Connections to other distant networks are implemented via point-to-point links originally implemented as part of the telephone network, or other WANs.
• voice and data networks converge digital techniques in telephone and mobile telephony networks.

Local Area Networks (LANs)

• LANs operate within a limited geographical area, allowing for different network structures and data access methods compared to larger networks.
• LAN design considerations include network topologies, access techniques, and the parameter, which relates to the ratio of data propagation time to data packet duration.
• Common protocols must be used for computers to be able to communicate effectively.
• Standardization is often based on the ISO Open Systems Interconnection (OSI) model, which provides a structured approach to network communication

The OSI Model and Layered Network Architecture

• Architecture: A system's rules and conventions.
• Protocol Stack: Protocols governing communications.
• The OSI model organizes communication into layers for easier function management and upgrading.

Layered Communication

• Entities at the same OSI layer communicate via an N-layer protocol, creating a virtual communication path.
• Communication goes through the layer and back up at the destination end.
• Each layer adds control (header) information which gets removed by corresponding layer at the receiving end.

Layer Operations

• Each layer is a SERVICE PROVIDER to the layer, and a SERVICE USER to the layer below it.
• N services are given to N+1 entities via SAPs logical interfaces.
• The interaction is managed with SERVICE PRIMITIVES, creating headers.

OSI Model: Lower Layers

• The lower layers depend on the physical technology used and are network dependant
• Physical Layer (Layer 1): Sends raw bits (1s and 0s) over a physical connection, including bit synchronization, cable types, connector shapes, and electrical signal levels.
• Data-Link Layer (Layer 2): Provides reliable data transfer by organizing bits into frames, error checking, and flow control, employing character-oriented or bit-oriented protocols.
• Network Layer (Layer 3): Determines the best data path between devices on different networks including switching and routing.

OSI Model: Upper Layers

• Operate at the host level
• Application: Semantics of app and allows user access by CASES and SASEs
• Presentation: Independence of the data by syntax and provides encryption.
• Session: Structures dialogue and establishes synchronization points and address mapping.
• Transport: Provided end to service communications.

Network Topologies

• Devices are connected in different structures (topologies) depending on how devices are connected.
• Mesh Networks:
  • Devices are connected to multiple devices and are used in packet-switched WANs
• Hierarchical Networks:
  • Tree like structure for connections, used commonly in telephone systems
• Routing and Switching:
  • Decisions on data flow between devices on where to send data for effective transfer of data

Star Configuration

• Every device connects to a central node through point-to-point connections
• The node controls all communications send to the correct device
• Intergrates easily with phone systems
• High speed connections can occur and can be used with single access control
• The central not takes most off the burden of workload and if it fails, the network is affected.

Bus Topology

• Devices are connected together with a single cable
• Signal is heard by all transmitted devices
• Processing, packetization, and access control is needed for all devices
• Easy for new units to connect and single failures doesn't affect the network
• However, cables could reduce bandwidth due to attenuation and is shared amoungst users
• Data gets transmitted by all devices and each device needs to consider whether they need it or not

Ring Topology

• Repeaters are joined by point-to-point links to close the loop
• Data is sent in sequence by each device
• Is easy to install and has efficient use of bandwidth
• Not easy to troubleshoot and has limited scalability

Topologies using Hubs

• Central Node (HUB) is passive, with bus or rings
• usually contains repeater electronics to enable longer link distance

Multiple Access: Broad Categories

• Based on the topology of LAN to give rise to methods of sharing network.
• Fixed Assignment: Channels allocated are static.
• Random/Contention Access: bandwidth is accessed randomly leading to packet collisions.
• Scheduled Access: methods can be centrally and can be distributed depending on how many devices that need use cases
• Adaptive Strategies can accommodate for demands on new networks

ALOHA

• a protocol was developed c.1970 for a packet-radio broadcast network at the University of Hawaii and does not have a LAN concept to local networking. It is a very simple, purely random access protocol.
• Receiving checks for valid frames
• Invalid frames can be caused by*:
• Channel noise.
• Another interference in transmission.

Pure-ALOHA

• A packet is effectively transferred if no other frames are transferred before "P"
• meaning P transmission time giving "2P" for period.

Network performance measures

• Measured in terms of data transfer through units
• normalising: s= λp/ r
• Throughput express in terms of offered load: G = λr/ r

Performance of pure - aloha

• Throughput = offered load . prob. of transmisions done succesfully
• Using G = λp,

Slotted ALOHA

Time is grouped into units to:

• Reduce period known as vulnerable
• Increase throughput

Performance of Aloha protocols

• The throughput lowers due to greater collision rate
• Retransmission rises and offered rises as well

Transmission attempts & Random retransmission delays

• Algoriths are often used when it deals with packet collisions
• Tends to give more throughput

Effect of propagation data delay (at distance)

• Vulerable time period rises to consider data delay period

Carrier sense multiple access (CSMA)

• Stations knowledgable of of packet transmissions
  • follow a Listen Before Talk protocol
  • Vulnerable time period is reduced to delay network
• Protocols are "slotted".
• Randomn distributed transmissions follow collisions

Basic CSMA Protocols :

• Non persistent
  • Where transmissions wait for random time
• Persistent
  • Waits for collisions for for channel
• P- persistent proctocols
  • Used w/ a slotted scheme and transmissions are done using this setup

Graphs of throughput as function of load

Different persistences compare with load Show that Non-Persistent have better peak throughput compared to other

Explore fundamental concepts of computer networks with focus on network architectures, protocols, and networking devices. Compare connection-oriented vs connectionless services. Master troubleshooting connectivity, performance, and reliability issues.